Chat Application

Client 1 ──┐ Client 2 ──┤──→ Server (ChatServer.java) ──→ Broadcast to all Client 3 ──┘

import java.io.*; import java.net.*; import java.util.*; import java.util.concurrent.*; public class ChatServer { private static final int PORT = 12345; private static Map<String, PrintWriter> clients = new ConcurrentHashMap<>(); public static void main(String[] args) throws IOException { System.out.println("Chat Server start ho gaya port " + PORT + " par..."); ExecutorService pool = Executors.newCachedThreadPool(); try (ServerSocket serverSocket = new ServerSocket(PORT)) { while (true) { Socket clientSocket = serverSocket.accept(); pool.execute(new ClientHandler(clientSocket)); } } } static void broadcast(String message, String senderName) { clients.forEach((name, writer) -> { if (!name.equals(senderName)) writer.println(message); }); } static void sendPrivate(String message, String toUser, String fromUser) { PrintWriter writer = clients.get(toUser); if (writer != null) { writer.println("[Private from " + fromUser + "]: " + message); } } static void addClient(String name, PrintWriter writer) { clients.put(name, writer); broadcast("📢 " + name + " chat mein join ho gaya!", name); System.out.println("New client: " + name); } static void removeClient(String name) { clients.remove(name); broadcast("📢 " + name + " chat se chala gaya.", name); System.out.println("Client left: " + name); } static String getUserList() { return "Online users: " + String.join(", ", clients.keySet()); } // ClientHandler — Har client ke liye alag thread static class ClientHandler implements Runnable { private Socket socket; private PrintWriter out; private BufferedReader in; private String username; ClientHandler(Socket socket) { this.socket = socket; } @Override public void run() { try { in = new BufferedReader(new InputStreamReader(socket.getInputStream())); out = new PrintWriter(socket.getOutputStream(), true); // Username lo out.println("Apna username enter karo:"); username = in.readLine(); if (username == null || username.trim().isEmpty()) { socket.close(); return; } username = username.trim(); if (clients.containsKey(username)) { out.println("Username already liya hua hai. Dobara try karo."); socket.close(); return; } addClient(username, out); out.println("Welcome " + username + "! Commands: /list, /pm @user msg, /quit"); String message; while ((message = in.readLine()) != null) { if (message.equalsIgnoreCase("/quit")) break; else if (message.equalsIgnoreCase("/list")) out.println(getUserList()); else if (message.startsWith("/pm ")) { // Private message: /pm @username message String[] parts = message.split(" ", 3); if (parts.length == 3) { String toUser = parts[1].replace("@", ""); sendPrivate(parts[2], toUser, username); } } else { broadcast("[" + username + "]: " + message, username); } } } catch (IOException e) { System.out.println("Error with client " + username); } finally { if (username != null) removeClient(username); try { socket.close(); } catch (IOException e) {} } } } }